The present invention relates to a lubricating oil composition for two-cycle engines, which is excellent in biodegradability, miscibility with gasoline, anti-seizure performance, and detergency at high temperature, and can be reduced in viscosity at low temperature as well.
Engine oil--in which an inexpensive mineral oil type of lubricating oil is used as the base oil and which may optionally contain cleaners and anti-wear agents--has been widely used. Lubricating oil used with two-cycle engines for motorcycles, outboard motors, etc., on the other hand, is now increasingly required to have miscibility with gasoline and anti-seizure performance, especially biodegradability. Unburned lubricating oil discharged from two-cycle engines are now known to pollute sea, and lakes and marshes, posing grave environmental problems. In other words, there is a strong demand for lubricating oil that has a high engine oil function well-enough to ensure that the required properties are achievable in small quantities, and is biodegradable as well, so that, when discharged into water, it can be easily degraded by water microorganisms.
In view of such situations, there has recently been developed a biodegradable type of lubricating oil which is mainly made up of a well-biodegradable polyol ester and in which an oil diluent such as kerosene or hydrogenated mineral oil is incorporated so as to assure miscibility with gasoline (see JP-A-4-120195). However, oil products containing a hydrocarbon type base oil as the oil diluent are still less than satisfactory in terms of biodegradability, due to its low biodegradability.
A so-called separate lubrication mode--in which fuel is mixed with lubricating oil in a two-cycle engine--has also been proposed. However, problems associated with this mode are that the lubricating oil becomes poor in fluidity at low temperature, so that it cannot be well miscible with gasoline, and it becomes poor in detergency at high temperature, making the amount of deposits larger.
The first object of the invention is to provide a lubricating oil composition for two-cycle engines, which can be used as engine oil that is excellent not only in biodegradability but also in miscibility with gasoline, anti-seizure performance and detergency.
The second object of the invention is to provide a lubricating oil composition for two-cycle engines, which can be used as engine oil that is particularly excellent in biodegradability.
The third object of the invention is to provide a lubricating oil composition for two-cycle engines, which has application in a wide range of temperatures; that is, which is excellent in detergency at high temperature, can be reduced in terms of viscosity at low temperature, and is improved in terms of miscibility with gasoline.